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BMW M30B34 specs: 3.4L (209 ci) 6-cylinder, 92 x 86 mm (3.6220 x 3.3858 in) bore and stroke, 8:1 compression. Rated 182 hp, 1985–1988.
The BMW M30B34 is oversquare — the 3.622" bore exceeds the 3.3858" stroke by 7.0% — a layout that favors airflow and RPM over leverage at the crank. The 3.3858" stroke does not reach 4,000 ft/min of mean piston speed until about 7,100 RPM, so piston speed is not what limits this engine's revs — valvetrain and breathing are. Each of the 6 cylinders displaces 34.8 ci (571 cc).
8:1 is low by modern standards and generally happy on regular pump fuel.
It is one of 2 engines in the BMW 209ci family, all of them 209 ci — the differences between them are in compression, heads and rating, not displacement. 7 factory variants share these dimensions, rated at 182 hp across 1985–1988.
| Displacement | 209 ci / 3.4 L |
|---|---|
| Bore | 3.622" |
| Stroke | 3.3858" |
| Cylinders | 6 |
| Configuration | I6 |
| Compression ratio | 8:1 * |
| Bore/stroke ratio | 1.07 |
* Compression ratio from a single source; not yet cross-verified.
| Fuel type | gas |
|---|---|
| Advertised HP | 182 hp |
| Years | 1985–1988 |
| Year | Version | HP @ rpm | Torque @ rpm | Comp. |
|---|---|---|---|---|
| 1985 | M30B34 net | 182 | — | — |
| 1986 | M30B34 net | 182 | — | — |
| 1987 | M30B34 net | 182 | — | — |
| 1988 | M30B34 net | 182 | — | — |
Factory specification sheet.
| Bore/stroke character | 1.070 — oversquare — bore exceeds stroke, which favours higher RPM and larger valves |
|---|---|
| Mean piston speed at 6,000 RPM | 3,386 ft/min — conservative for a street engine |
| Displacement per cylinder | 34.8 ci |
| Static compression | 8:1 — low by modern standards, generally happy on regular pump fuel |
Each link opens the calculator with this engine's specs already filled in.
These records share identical bore, stroke, displacement and compression. They differ by model year and factory power rating.
| Year | Advertised HP | Code |
|---|---|---|
| 1985 | — | M30B34 |
| 1985 | 182 hp | M30B34 |
| 1986 | — | M30B34 |
| 1986 | 182 hp | M30B34 |
| 1987 | — | M30B34 |
| 1987 | 182 hp | M30B34 |
| 1988 | 182 hp | M30B34 |
3 factory vehicles, 1985–1988. Each year opens that model's engine table.